[Haskell] lhs2TeX: lazy pattern "~" formatting

[Conal Elliott]

Does anyone have a nice way to format the "~" of a lazy pattern in
lhs2TeX?  I use

  %format ~ = "{} ^\sim "

but the result isn't as pretty as I'd like.  For one thing, no space
is inserted before the "~" after a lambda, "do", or whatever.

Thanks,  - Conal